The present invention generally relates to the field of diverters used in marine seismic operations. More particularly, the present invention relates to diverters having vortex generators to prevent stall at high attack angles.
Marine seismic diverters control movement of seismic streamers and other equipment relative to a seismic tow vessel. As the tow vessel moves through the water, an array of one or more streamers and/or other equipment carrying cables are towed at a known velocity through the water. For multiple cables, diverters pull the cables outwardly from the vessel centerline to establish a separation among cables and maintain a width or xe2x80x9cspreadxe2x80x9d for the streamer array.
Marine seismic diverters typically have wing shaped sections extending into the water (commonly referred to as xe2x80x9cvanesxe2x80x9d) for urging the diverter and attached cable away from the seismic array centerline. The lateral displacement forces exerted by the vanes depend on the tow vessel speed, shape of the vane, and the angle at which the leading edge of the vane meets the oncoming flow of water (commonly referred to as the xe2x80x9cattack anglexe2x80x9d). For example, increasing the attack angle may increase the lateral displacement force proportionally and lead to an increased spread of the seismic array.
Increasing the spread of the seismic array may reduce seismic exploration costs by reducing a number of passes necessary to gather seismic data for a given area. Using relatively high attack angles, spreads of over one kilometer are achievable. However, if the attack angle becomes too great, the diverters may stop exerting lateral displacement forces and stall, which may result in a collapse of the spread, loss of cable separation, and, possible damage to the streamers, which may be extremely expensive to replace. Further, significant personnel time may be required to retrieve and re-deploy the streamer array resulting in costly delays in data gathering operations.
Accordingly, a need exists for a seismic diverter that avoids stall at high attack angles.
The present invention generally provides an apparatus, system, and method for deflecting one or more cables towed behind a vessel.
Embodiments of the apparatus comprise an attached or detached float with at least one vane shaped to move a cable in a selected direction as the vessel tows the cable through the water. One or more vortex generators are disposed on the vane to generate small vortexes within a boundary layer of laminar water flow across the vane to prevent boundary layer separation and the onset of stall at high attack angles. Some embodiments may comprise a controller capable of adjusting an attack angle of the diverter vane and/or a location of the vortex generators.
Embodiments of the system may comprise at least two such diverters attached to opposing outer cables of an array of cables towed behind a vessel. The diverters may provide opposing lateral forces for moving the opposing outer cables in opposing outer directions, creating a spread for the array. Embodiments of the method may comprise attaching the diverters to opposing outer cables and/or cables within the array and adjusting an attack angle of the diverters and/or a location of the vortex generators as the vessel tows the array of cables through the water.